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About some days ago the internet stopped working.

I noticed that if I manually changed the DNS to OpenDNS's IPs, or Google Public DNS's IPs, on the Network Settings, the internet worked again.

If the router is left alone to solve the DNS by itself, without manually setting a Public DNS, the internet doesn't work.

This problem seemed to start some days ago when to router updated itself.

EDIT:

I've set the Google Public DNS's directly on the router, but when I remove these DNS's from the local configuration on the computer, leaving it blank, the internet still doesn't navigate, even after cleaning the cache (dscacheutil -flushcache).

RESOLUTION:

It turns out that the router was solving DNS correctly, the problem was on the switcher device which was messing up with the DNSs when redistributing them.

Reseting the switcher to its factory default settings solved the problem.

Anyway, we now use OpenDNS's public DNS just in case something similar happens again.

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The DNS settings from before were probably using your ISP's servers. During the update, they may have been lost. You can manually specify them (look them up for your area) or use Google's or OpenDNS at the router level to fix it manually. Some routers have a magic refresh button that tries to resolve them from a modem, if you have one. –  nerdwaller Nov 22 '13 at 16:27
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I'm quite sure the Internet is still working. Maybe your connection is not. ;) –  Envite Nov 22 '13 at 16:31
    
Plus one for pairing the title with an actual competent question :) –  Yitzchak Nov 22 '13 at 17:26

2 Answers 2

Every "router" (nat device) I have ever used had problems with dns, so I always run a local dns server or two, which also allows me to setup lan dns (this allows you to connect to your local computers by name without messing with hostfiles).

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What kind of routers are you using that you have to do that? Every router I had- I made sure that DHCP was enabled so the build in DNS server knew what computers connected to it. Also forget about static private IP's because that also messes up routers DNS. Some or stupid but newer routers have "preffered ip address" under DHCP- DNS works like a dream. I only used hosts files for testing live websites on debugging... –  ppumkin Nov 28 '13 at 17:23
    
I mostly have been using actiontec dsl boxes provided by the phone company, and I run my own dhcp server for netbooting, so it all just works. –  hildred Nov 28 '13 at 17:31

When you have your router act as the DNS server it uses your ISP's DNS servers. If your ISP's DNS servers are offline and or not resolving for the IP you are trying to reach, it will appear your internet is down. Using public DNS servers like google (8.8.8.8/8.8.4.4) or others is a way of potentially getting better up-time an or resolution. My guess is your ISP's DNS servers are/where down, or there was a problem with the router upgrade and DNS servers did not make the cut.

What is a DNS Server:

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